1. Field of the Invention
The invention relates to the field of analog integrated filters and filtering methods, particularly filters utilizing switched capacitor techniques.
2. Prior Art
Substantial amounts of effort have been expended in the development of circuitry and methods for the digitization of analog information for digital transmission. In order to achieve high quality audio application in analog-to-digital encoders and decoders, voiceband filters are required which must meet among other stringent requirements, stringent signal-to-noise ratios and power supply rejection. Degradation of monolithic filter performance has been a particular problem. In an integrated filter, the amount of power dissipation, supply rejection and signal-to-noise ratio is appreciably different than the amounts experienced in circuits comprised of passive or discrete active elements. In addition, integrated filters are subject to chip area limitations. However, in order to devise an economical and effective device in digital communications, it is indispensable that a circuit design and methodology, operable within the design limitations of an integrated circuit, be realized.
What is needed then is a circuit and method by which a combination of filter and analog-to-digital encoder, and of filter and digital-to-analog decoder can be devised in an integrated circuit to meet the stringent requirements with respect to noise and power supply rejection imposed upon the circuit by voice transmission standards and still meet the power dissipation and chip area limitations inherent in integrated circuit design.